1. Field of the Invention
The present invention relates to a method for preparing a laminate such as a plywood or an LVL (laminated veneer lumber). The method uses veneers to prepare a laminate substantially free from warp.
2. Description of the Prior Art
The applicant of the present application has previously proposed a method for preparing a laminate that undergoes only a little or no substantial warp, which comprises symmetrically laminating via an adhesive two veneers having substantially the same grains with respect to the center line in the thickness direction of the laminate to be prepared (Japanese Unexamined Patent Publication No. 185402/1990).
According to this method, if tensile or compressive forces are caused due to extension or contraction of the veneers themselves during or after the preparation thereof or contraction by curing of the adhesive, the tensile or compressive forces are symmetrically balanced with respect to the center line in the direction of the thickness of the laminate. Accordingly, if veneers made of a wood of a kind which undergoes considerable warp or the like by drying (for example, Radiata Pine) are used, a laminate which undergoes only a little warp.
In the above preparation method, an undried veneer is divided in its thickness direction with a divider such as a blade to obtain two veneers having substantially the same grains (hereinafter referred to as counter veneers), and the counter veneers are dried to water contents of 5 to 15% which are suitable for bonding, and the dried counter veneers are superposed on another ligneous board as a center in a manner as described above, and the resultant is heat-pressed by means of a hot press to complete bonding. However, the method has the following problems.
When a veneer made of a wood of a kind which undergoes considerable warp or the like by drying is used, dried counter veneers can be prevented from being appropriately transferred to a predetermined place due to occurrence of warp or the like. Further, it is difficult to manually or mechanically superpose the counter veneers in the above-mentioned symmetrical relationship with precision. These lead to problems of lowered yield and impaired quality of the product. To overcome the problems, it has been attempted that undried counter veneers are superposed, without being dried after the division, on another ligneous board as a center via an adhesive and the resultant is heat-pressed. However, if the counter veneers have high water contents, bonding failure is caused. Accordingly, a satisfactory laminate cannot be obtained.